Interfacial processes for the polymerization of polycarbonates yield a mixture comprising an aqueous phase and an organic phase. The aqueous phase, also referred to as the brine phase, comprises salts, ionic species, and interfacial catalyst. The organic phase, also referred to as the resin phase or polymer phase, comprises solvent, dissolved polycarbonate, and interfacial catalyst. Some salts and ionic species (collectively, “ions”) can further be present in the organic phase as a result of brine entrainment from the aqueous phase. These ions, as well as any interfacial catalyst are generally removed from a separated organic phase in a purification process as they affect the final product quality. Such a purification process generally involves separation of the aqueous phase from the organic phase followed by the removal of catalyst and ions in one or more extraction steps to result in a purified polycarbonate.
In order to obtain efficient separation at economical throughputs, a typical process uses a series of high revolution per minute (rpm) disk stack centrifuges. Centrifuges are effective for separations but are expensive. They also tend to require significant electrical energy input and have maintenance costs. Emulsification is another problem that can impact the purification process, particularly in the purification of some copolycarbonates.
A purification process with lower cost, improved separation, or both is desirable.